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authorTorstein Hegge <hegge@resisty.net>2013-03-26 22:10:05 +0100
committerTakashi Iwai <tiwai@suse.de>2013-04-03 17:05:44 +0200
commit690a863ff03d9a29ace2b752b8f802fba78a842f (patch)
treeae4e3032c9b17fbd355776557bfc24e498e37e82 /sound
parent10250911c6f3531e9c2f4f1c6017782bc9bcd6d4 (diff)
downloadvexpress-lsk-690a863ff03d9a29ace2b752b8f802fba78a842f.tar.gz
ALSA: usb: Work around CM6631 sample rate change bug
The C-Media CM6631 USB receiver doesn't respond to changes in sample rate while the interface is active. The same behavior is observed in other UAC2 hardware like the VIA VT1731. Reset the interface after setting the sampling frequency on sample rate changes, to ensure that the sample rate set by snd_usb_init_sample_rate() is used. Otherwise, the device will try to use the sample rate of the previous stream, causing distorted sound on sample rate changes. The reset is performed for all UAC2 devices, as it should not affect a standards compliant device, but it is only necessary for C-Media CM6631, VIA VT1731 and possibly others. Failure to read sample rate from the device is not handled as an error in set_sample_rate_v2(), as (permanent or intermittent) failure to read sample rate isn't essential for a successful sample rate set. Signed-off-by: Torstein Hegge <hegge@resisty.net> Acked-by: Clemens Ladisch <clemens@ladisch.de> Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'sound')
-rw-r--r--sound/usb/clock.c45
1 files changed, 35 insertions, 10 deletions
diff --git a/sound/usb/clock.c b/sound/usb/clock.c
index 5e634a2eb28..9e2703a2515 100644
--- a/sound/usb/clock.c
+++ b/sound/usb/clock.c
@@ -253,7 +253,7 @@ static int set_sample_rate_v2(struct snd_usb_audio *chip, int iface,
{
struct usb_device *dev = chip->dev;
unsigned char data[4];
- int err, crate;
+ int err, cur_rate, prev_rate;
int clock = snd_usb_clock_find_source(chip, fmt->clock);
if (clock < 0)
@@ -266,6 +266,19 @@ static int set_sample_rate_v2(struct snd_usb_audio *chip, int iface,
return -ENXIO;
}
+ err = snd_usb_ctl_msg(dev, usb_rcvctrlpipe(dev, 0), UAC2_CS_CUR,
+ USB_TYPE_CLASS | USB_RECIP_INTERFACE | USB_DIR_IN,
+ UAC2_CS_CONTROL_SAM_FREQ << 8,
+ snd_usb_ctrl_intf(chip) | (clock << 8),
+ data, sizeof(data));
+ if (err < 0) {
+ snd_printk(KERN_WARNING "%d:%d:%d: cannot get freq (v2)\n",
+ dev->devnum, iface, fmt->altsetting);
+ prev_rate = 0;
+ } else {
+ prev_rate = data[0] | (data[1] << 8) | (data[2] << 16) | (data[3] << 24);
+ }
+
data[0] = rate;
data[1] = rate >> 8;
data[2] = rate >> 16;
@@ -280,19 +293,31 @@ static int set_sample_rate_v2(struct snd_usb_audio *chip, int iface,
return err;
}
- if ((err = snd_usb_ctl_msg(dev, usb_rcvctrlpipe(dev, 0), UAC2_CS_CUR,
- USB_TYPE_CLASS | USB_RECIP_INTERFACE | USB_DIR_IN,
- UAC2_CS_CONTROL_SAM_FREQ << 8,
- snd_usb_ctrl_intf(chip) | (clock << 8),
- data, sizeof(data))) < 0) {
+ err = snd_usb_ctl_msg(dev, usb_rcvctrlpipe(dev, 0), UAC2_CS_CUR,
+ USB_TYPE_CLASS | USB_RECIP_INTERFACE | USB_DIR_IN,
+ UAC2_CS_CONTROL_SAM_FREQ << 8,
+ snd_usb_ctrl_intf(chip) | (clock << 8),
+ data, sizeof(data));
+ if (err < 0) {
snd_printk(KERN_WARNING "%d:%d:%d: cannot get freq (v2)\n",
dev->devnum, iface, fmt->altsetting);
- return err;
+ cur_rate = 0;
+ } else {
+ cur_rate = data[0] | (data[1] << 8) | (data[2] << 16) | (data[3] << 24);
}
- crate = data[0] | (data[1] << 8) | (data[2] << 16) | (data[3] << 24);
- if (crate != rate)
- snd_printd(KERN_WARNING "current rate %d is different from the runtime rate %d\n", crate, rate);
+ if (cur_rate != rate) {
+ snd_printd(KERN_WARNING
+ "current rate %d is different from the runtime rate %d\n",
+ cur_rate, rate);
+ }
+
+ /* Some devices doesn't respond to sample rate changes while the
+ * interface is active. */
+ if (rate != prev_rate) {
+ usb_set_interface(dev, iface, 0);
+ usb_set_interface(dev, iface, fmt->altsetting);
+ }
return 0;
}